假如用户的数据库是ORACLE SQL ACCESS中的一个，如何选择性的实现到用户特定数据库的连接？如何封装？

答案：JAVA数据库工具类，读取数据源，配置文件的方法都有，GOOD LUCK!
import java.util.List; 
import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.Properties; 
import java.util.Collections; 
import java.io.*;
import java.sql.Connection; 
import java.sql.SQLException; 
import java.sql.ResultSet; 
import java.sql.ResultSetMetaData; 
import java.sql.Statement; 
import java.sql.PreparedStatement;
import java.sql.DriverManager; 
import javax.naming.Context; 
import javax.naming.InitialContext; 
import javax.naming.NamingException; 
import javax.sql.DataSource; 
public class DBUtil{
 public String db_ip;
 public String db_port;
 public String db_uid;
 public String user;
 public String password;
 public String db_driver;
 public String db_url;
 public String db_type;
 public String Sqlstring;
 public Connection db_conn;
 public Statement db_stmt;
 public ResultSet db_rset;
 public int record_count;
 public int page_count;
 public int rows_perpage;
 public int current_page;
 public int current_page_rows;
 /**
 * 通过数据源连接数据库
 * @param datasourcename String
 */
 public void dbconnbyDatasource(String datasourcename){
 try {
 Context initContext = new InitialContext();
 DataSource ds = (DataSource) initContext.lookup(datasourcename);
 db_conn = ds.getConnection();
 db_stmt = db_conn.createStatement();
 } catch (Exception e) {
 System.out.println("数据库连接错误："+datasourcename);
 }
 }

 /**
 直接获取数据源，
*/
public void getdbconnDatasource(){
dbconnbyDatasource("PortalDataSource");

}

 /**
 * 通过配置文件连接数据库
 * @param datasourcename String
 */
public void dbconnbyFile(String filename){
 File file = new File(filename);
 String s = file.getAbsolutePath().replace('\\', '/');
 Properties properties = new Properties();
 try {
 FileInputStream fileinputstream = new FileInputStream(s);
 properties.load(fileinputstream);
 if(fileinputstream != null)
 fileinputstream.close();
 }
 catch(IOException ioexception) {
 System.out.println("不能打开配置文件："+filename);
 return;
 }
 db_type = properties.getProperty("db_type");
 user = properties.getProperty("user");
 password = properties.getProperty("password");
 byte byte0 = 2;
 if(db_type.equals("oracle"))
 byte0 = 1;
 switch(byte0)
 {
 default:
 break;
 case 1: // '\001'
 db_ip = properties.getProperty("db_ip");
 db_port = properties.getProperty("db_port");
 db_uid = properties.getProperty("db_uid");
 try {
 Class.forName("oracle.jdbc.driver.OracleDriver");
 }
 catch(ClassNotFoundException classnotfoundexception)
 {
 System.out.println("Could not load the driver.");
 }
 String s1 = user + "/" + password + "@" + db_ip + ":" + db_port + ":" + db_uid;
 try {
 db_conn = DriverManager.getConnection("jdbc:oracle:thin:" + s1);
 db_stmt = db_conn.createStatement();
 }
 catch(SQLException sqlexception) {
 System.out.println("Creat connection error.");
 }
 break;
 case 2: // '\002'
 db_driver = properties.getProperty("db_driver");
 db_url = properties.getProperty("db_dsn");
 try {
 Class.forName(db_driver);
 }
 catch(ClassNotFoundException classnotfoundexception1) {
 classnotfoundexception1.printStackTrace();
 }
 try {
 db_conn = DriverManager.getConnection(db_url, user, password);
 db_stmt = db_conn.createStatement();
 }
 catch(SQLException sqlexception1) {
 System.out.println("Creat connection error.");
 }
 break;
 }
 }

 /**
 * 关闭数据库连接
 */
 public void dbClose(){
 if (db_rset != null) try{ 
 db_rset.close(); 
 }catch(java.sql.SQLException ex){ 
 ex.printStackTrace(); 
 } 
 if (db_stmt != null) try{ 
 db_stmt.close(); 
 }catch(java.sql.SQLException ex){ 
 ex.printStackTrace(); 
 } 
 if (db_conn != null) try{ 
 db_conn.close(); 
 }catch(java.sql.SQLException ex){ 
 ex.printStackTrace(); 
 } 
 }

 /**
 * 执行更新、插入、删除、建表等不需要返回结果的SQL语句
 */
 public int executeSql(String updatesql) throws SQLException {
 int i=0;
 Statement db_stmts = db_conn.createStatement();
 i= db_stmts.executeUpdate(updatesql);
 db_stmts.close();
 return i;
 }


 /**
 * 执行select语句，返回结果数据集List
 */
 public List queryDatalist(String querystr) throws SQLException {
 countRecord(querystr);
 if (record_count == 0)
 return null;
 Statement db_stmts = db_conn.createStatement();
 db_rset = db_stmts.executeQuery(querystr);
 List list = resultSetToList(db_rset);
 db_stmts.close(); 
 return list; 
 }
 /**
 * 执行select语句，返回结果数据集ResultSet
 */
 public ResultSet queryResultset(String querystr) throws Exception {
 countRecord(querystr);
 if (record_count == 0)
 return null;
 db_rset = db_stmt.executeQuery(querystr);
 return db_rset;
 }

 /** 
 * 将查询结果封装成List。br 
 * List中元素类型为封装一行数据的Map，Map key为字段名（大写），value为相应字段值 
 * @param rs ResultSet 
 * @return List 
 * @throws java.sql.SQLException 
 */
 public List resultSetToList(ResultSet rs) throws SQLException{ 
 if (rs==null) return Collections.EMPTY_LIST; 
 ResultSetMetaData md = rs.getMetaData(); 
 int columnCount = md.getColumnCount(); 
 List list = new ArrayList(); 
 HashMap rowData;
 current_page_rows = 0; 
 while (rs.next()){ 
 rowData = new HashMap(columnCount); 
 for (int i=1; i=columnCount; i++){ 
 rowData.put(md.getColumnName(i).toLowerCase(),rs.getObject(i)); 
 } 
 list.add(rowData); 
 current_page_rows++;
 } 
 return list; 
 } 

 
}

其他：1.定义3个连接方式
2.根据数据库的type，以及id区别连接方式
3.封装方式很重要，这里面的参数取决于你的链接方式

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